1. Field
Example embodiments relate to a memory device, and more particularly, to a doped phase change material doped and a phase change memory device including the phase change material.
2. Description of the Related Art
A phase change memory device (PRAM) is a type of non-volatile memory device such as a ferrodielectric RAM (FeRAM) and a magnetic RAM (MRAM), for example. The difference of the PRAM from other non-volatile memory devices lies in a storage node of the PRAM.
Generally, the storage node of the PRAM includes a phase change layer that changes from a crystalline state to an amorphous state at a first temperature, and changes from an amorphous state to a crystalline state at a second temperature that is lower than the first temperature.
The resistance of the phase change layer when the phase change layer is in an amorphous state is referred to herein as a first resistance, and the resistance of the phase change layer when the phase change layer is in a crystalline state is referred to herein as a second resistance. Generally, the first resistance is larger than the second resistance.
A conventional PRAM writes and reads data by using the characteristics of the resistance of the phase change layer. The resistance of the phase change layer may change based on the state of the phase change layer. Presently, a Ge2Sb2Te5 (GST) layer is widely used as the phase change layer of a conventional PRAM.
Generally, an ideal phase change material is considered to be a material that has low thermal conductivity and a low melting point at which the phase changes from the crystalline state to the amorphous state. Further, the ideal phase change material has a high resistance when the phase is amorphous and a high crystallization temperature at which the phase changes from the amorphous state to the crystalline state in order to obtain thermal stability.
However, the GST layer has a melting point that is greater than 600° C. and a relatively low resistance. Accordingly, in the case of the conventional PRAM in which the GST layer is used as the phase change layer, a high reset current to change a portion of the phase change layer into an amorphous state must be applied. In the conventional PRAM, the GST layer changes from the amorphous state to the crystalline state at about 160° C. Thus, the GST layer of the conventional PRAM cannot be used in the case where a high thermal stability is required.